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Nov. 1, 2012 (Boston) -- A pricey new treatment for prostate cancer called proton beam therapy appears to cause slightly less diarrhea, bloating, and cramping than traditional radiation treatments. But the effect is short-lived, a new study suggests.

The findings come from a review of questionnaires filled out by men who underwent one of three forms of radiation therapy, so the results are far from conclusive.

But even though proton beam therapy's effectiveness and safety has yet to be proven, more and more men are opting for the treatment. The number of treatments has climbed steadily in the last five years and is expected to double in the next three years, says researcher Phillip J. Gray, MD, a resident in the Harvard Radiation Oncology program in Boston.

"Patients say proton beam therapy sounds so much better, they want it no matter what the cost," says Colleen Lawton, MD, a radiation oncologist at the Medical College of Wisconsin Clinical Cancer Center in Milwaukee.

"We don't know if it is less toxic. We don’t know if it is more effective. All we do know is that it is more costly."

Lawton, who was not involved with the research, moderated a news briefing to discuss the findings here at the annual meeting of the American Society for Radiation Oncology (ASTRO).

Bowel, Urinary Problems

In proton beam therapy, beams of protons are targeted directly to tumors, thereby sparing healthy tissue, which theoretically should cause fewer side effects. Indeed, its benefit in treating eye and pediatric brain tumors is well documented. But for prostate cancer, the answer is far less clear.

So Gray and colleagues studied three groups of men: 94 who got proton beam therapy, 153 who were treated with what's called intensity-modulated radiation therapy (IMRT), and 123 who were treated with an older form of external beam radiation that IMRT has replaced over the past decade.

Internal radiation therapy (also known as brachytherapy) was not included in this study.

IMRT also delivers its radiation with extremely high precision, thereby reducing the risk that it will hit surrounding healthy tissue -- but in this case the cargo is X-ray radiation, not protons.

By two to three months later, men treated with proton beam therapy reported minimal diarrhea and cramping compared with men in either of the other two groups.

But by one year later, men treated with proton beams had similar bowel problems, and that persisted out to the two years of the study.

All three groups had more urinary irritation and flow problems in the first few months of treatment than they did before the study started. Men given IMRT fared the worst, reporting bothersome urinary problems in the early months. "By two years out, all three groups had minimal, lingering problems," Gray says.

And all three groups reported worsening sexual function over the two years of the study.

The men weren't followed for long enough to know whether one treatment curbs tumor growth better than the others.

$32,500 Price Tag

A study reported at another cancer meeting last winter showed that men treated with proton beams later had about one-third more bowel problems, such as bleeding and blockages, than similar men given conventional radiation.

Proton beam therapy is about 70% more expensive than IMRT, says James Yu, MD, a radiation oncologist at Yale University in New Haven, Conn.

A review of Medicare claims data showed the average amount that Medicare reimbursed for proton beam therapy is about $32,500 vs. about $18,500 for IMRT.

These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.